The present invention relates to accelerometers. In particular, the present invention relates to electret-based accelerometers.
An accelerometer is a sensor that provides an electrical signal that is indicative of the acceleration experienced by the sensor. Examples of accelerometers include potentiometric, capacitive, inductive, optical and piezoelectric.
A capacitive accelerometer measures acceleration based on a change in the capacitance of some element in the sensor. One type of capacitive accelerometer is known as an electret-based accelerometers.
An electret-based accelerometer contains an electret, which is a permanently charged material that is an analogue to a permanent magnet. This permanently charged material is placed between a base plate and a metalized flexible diaphragm to form a charged capacitor. Either the base plate or the diaphragm is connected to a JFET transistor. As the diaphragm moves relative to the rest of the accelerometer, the capacitance of the capacitor changes thereby changing the output voltage of the JFET.
Under the prior art, electret accelerometers have been prone to producing noisy accelerometer signals especially in acoustically noisy environments. Thus, it is desirable to reduce the level of noise in the accelerometer signals.
Accelerometers are also relatively expensive to produce compared to other sensors found in electronic devices. As a result, it is desirable to reduce the cost of manufacturing accelerometers.